The present invention relates generally to power delivery systems and fabrication methods, and more particularly to power delivery systems between a step down converter and an integrated circuit, and methods of fabricating the same.
A requirement of most electronic systems is a regulated source of direct current (DC) voltage. Whether the DC power originates with a battery or has been converted from alternating current (AC) power, a voltage regulator circuit is usually required to provide a steady DC voltage having the correct amplitude. In some cases, however, AC power is supplied to the electronic system, in which case an AC distributor is employed to downconvert and frequency enhance the AC power.
Used in conjunction with an integrated circuit, a regulated source of power is typically provided using a step down converter (SDC), which can be, for example, a voltage regulator module (VRM) or an AC distributor. FIG. 1 illustrates a circuit 100 for supplying power to an integrated circuit load 108 in accordance with the prior art. Circuit 100 includes AC voltage source 102, SDC 104, and power delivery system 106.
Initially, voltage is supplied by AC voltage source 102. If SDC 104 is a VRM, the amplitude is then modified, and the resulting AC voltage is rectified, filtered, and regulated by SDC 104. In many cases, a separate analog-to-digital converter (not shown) is used to convert the AC power to DC before it is supplied to the VRM, whereupon the VRM steps the voltage down to a voltage required by the load 108. If SDC 104 is an AC distributor, the amplitude is modified and the frequency is enhanced before supplying the power to load 108. SDC 104 may be incorporated into a single discrete component, or may include multiple discrete components (e.g., voltage regulator, inductors, decoupling capacitors, rectifiers, etc.). The converted voltage is then supplied to load 108 through power delivery system 106. Load 108 could be, for example, one or more circuits within a microprocessor or some other type of integrated or discrete circuit.
Power delivery system 106 generally includes a series of conductive elements through which the power flows from SDC 104 to load 108. A voltage drop occurs between SDC 104 and integrated circuit load 108 due to losses along the path between SDC 104 and load 108. The voltage drop caused by power delivery system 106 can be roughly modeled by an inductor 110 in series with a resistor 112, which represent the inductance and resistance, respectively, of the conductive path between SDC 104 and load 108. In many cases, it is desirable to minimize these values in order to minimize the voltage drop that occurs through the power delivery system 106.
All other things being equal, the farther the distance between SDC 104 and integrated circuit load 108, the larger the voltage drop. At relatively low voltages, this voltage drop is a tolerable effect that is compensated for by providing an SDC that supplies a higher voltage than is actually needed by the integrated circuit. A negative side effect of this strategy, however, is that the SDC may need to be larger than necessary, and power is inefficiently consumed.
In some prior art configurations, to reduce the distance between the SDC 104 and the load 108, SDC 104 is mounted on a printed circuit (PC) board as close as practical to the integrated circuit package socket. In this configuration, current travels through traces in the PC board, and up through the socket and the package pins. The current continues along traces in the package to connections that make electrical contact with pads on the integrated circuit.
In some high performance applications, however, the electrical distance between a PC board mounted SDC and the integrated circuit is unacceptably far. One solution for reducing the electrical distance between the SDC and the integrated circuit is to mount the SDC on a power pod, and to connect the power pod to an interposer upon which the integrated circuit package is mounted.
FIG. 2 illustrates a schematic cross-section of an SDC 202 mounted on a power pod 204, and coupled to an interposer 206 via a connector 208 in accordance with the prior art. An interposer 206 essentially is a small PC board that enables other components to be mounted in close proximity to the integrated circuit, and/or that provides a dimensional interface between the connectors 210 to an integrated circuit package 212 and the pin holes of a PC board socket 214. Interposers are often used when the scale and/or location of connectors 210 are different from the scale and/or location of pin holes on the socket 214. In addition, in some cases, interposers may be used to house decoupling capacitors (not shown) or other small discrete components in close proximity to the integrated circuit package 212.
SDC 202 receives AC power and ground through pins 216 inserted into PC board 218. SDC 202 then regulates the power, as described above. The resulting voltage may then be filtered by an inductive filter and decoupling capacitors (not shown). That power is then supplied to integrated circuit 220. To supply power to the integrated circuit 220, electrical current travels from SDC 202 through traces (not shown) in power pod 204. The current then travels through connector 208 and additional traces (not shown) within interposer; 206, through connectors 210, and through still other traces (not shown) in integrated circuit package 212. Finally, the current reaches ball joints (or some other type of connector, such as bond wires), which electrically and physically connect integrated circuit 220 to package 212. Various loads (not shown) on the integrated circuit 220 may then consume the supplied power.
Unfortunately, connector 208 is a relatively high-inductance component, thus the performance of the power delivery system is reduced by its presence. In addition, connector 208 is a separate component, resulting in additional cost, reliability issues, and board, assembly procedures.
As frequencies, edge rates, and current demands of high performance integrated circuit products continue to increase, the inductance and resistance of the power delivery system become critical parameters. For the reasons stated above and for other reasons stated below, which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a lower-inductance power delivery system than has been achieved using prior art configurations. In addition, there is a need in the art for a power delivery system that is low-cost, reliable, and does not require significant changes in board assembly procedures.